Accommodative Intraocular Lenses — Mechanical Design

Cataracts, the clouding of the crystalline lens of the eye, are the leading cause of blindness in the world. Currently, the most effective treatment is to surgically remove the clouded lens and replace it with an artificial intraocular lens. This, however, induces presbyopia in patients because the IOL does not undergo accommodation like the natural lens. Patients require spectacles even after successful surgery. Aurolab wants to transform its current IOL technology into an accommodative IOL to provide patients with their full range of vision. Our goal was to develop a proof of concept for an apparatus that connects to a current Aurolab lens and gives it full accommodative power. We pursued a design that utilizes the geometric relationships between the sides of an isosceles triangle to create a passive shift single-optic accommodative IOL. We fabricated prototypes through 3D printing and laser cutting, and designed and constructed two haptic actuators to conduct trade studies on these prototypes: a 1x scale stepper motor actuator, and a 3x scale winch actuator. The more successful iteration, Delta, demonstrated over 3 mm of anterior movement, surpassing the benchmark for an accommodative IOL at the 3x scale.

Development of a Novel Inline Intravenous Fluid Sterilizer

Healthcare-associated infections (HAIs) affect more than one in 20 people who visit a healthcare facility in the United States. These infections cost billions of dollars and are responsible for over 1,000 deaths annually. Intraluminal bloodstream infections are an especially deadly type of HAI and account for over 6% of HAI-related deaths. Current preventative measures, such as manually scrubbing intravenous (IV) ports or covering them with passive sterilization caps, have proven insufficient to combat these infections.

B.B.R. Medical Devices has developed a concept for an inline fluid sterilizer that utilizes ultraviolet C (UVC) to sterilize fluid going into the patient. Our project iterates beyond BBR’s existing prototype. Our deliverables are: (1) an inline sterilizer housing and cassette prototype based on an inexpensive fluid warmer cassette design, and (2) pharmaceutical testing to provide initial data on the effect of UVC on selected pharmaceuticals. The cassette design was finalized as a two-piece assembly: a UVC opaque base thermoformed to the appropriate shape, and a flat, UVC transmissive material on top. The cassette and bulb are placed in the lower compartment, while the remainder of the electronics are placed in the upper compartment. This separation protects the electronics from degradation via UVC. Biological testing showed no growth after running E.coli cells through the device.

Device to Detect Staphylococcus aureus

Hospital-acquired infections (HAIs) kill nearly 100,000 people per year, in part because pathogens, most notably Staphylococcus aureus, remain undetected on hospital surfaces. There is a need for a rapid, easy-to-use device that can detect and identify S. aureus on hospital surfaces both before and after cleaning. The deliverables of the project are: a working prototype of a portable, easy-to-use device that quickly detects and identifies a critical dose of S. aureus on hospital surfaces, and a business model with market, manufacturing, and stakeholder analysis of the final device. The proposed solution consists of a lateral flow strip housed in an easy-to-use mechanical user interface. The user swabs a surface, inserts the swab handle into the housing, and releases the contents of the swab onto the strip. Any S. aureus cells bind to antibodies in buffer in the housing. Within two minutes the user can read the results: two red lines indicate that S. aureus is present in the sample; one red line indicates a negative test. An in-depth economic analysis and business plan has verified that the device is not only technologically valid, but it is also marketable.

Electrical Impedance Measurement of a Fetal Heartbeat

Obstetricians and gynecologists frequently monitor fetal heart rate (FHR) to detect problems in the health of a fetus during pregnancy and labor. Doppler measurement is the current best-practice among the state-of-the-art, but patients and doctors find it difficult to use continuously. Continuous monitoring of the fetal heart rate would allow doctors to observe variations in the fetal heart rate over time, and variation in fetal heart rate has been correlated with positive health outcomes.

Our sponsor proposes to use electrical impedance (EI) to measure FHR. This novel solution theoretically allows continuous monitoring, but our sponsor needs a testing apparatus to develop the device, and benchmark testing is needed for implementation into the healthcare system. In response, we delivered a physical model of the human womb and fetus that is suitable for electrical impedance research.

We developed a finite element simulation of the womb and fetus to inform development of a physical model capturing electrical, fluid, and geometric properties. Four components needed to be represented: tissues held in quasi-static conditions, the beating fetal heart, the beating maternal heart, and motion artifacts such as gait. We constructed the model as four discrete systems. The model is highly parametric, giving the sponsor the ability to easily (1) change layer impedance, (2) change heart rates, (3) change stroke volume, (4) introduce different motion artifacts, and (5) change electrode materials and locations, in order to model a variety of patient conditions. The project came in under budget and carries significant economic potential as a research device for the sponsor’s own research and as a commercial product for the scientific community.

The project also won the 2014 Northeast Bioengineering Conference Undergraduate Design Competition.

Electrical Impedance Monitoring of Brain Tissue

In the United States alone, traumatic brain injury (TBI) causes roughly 230,000 hospitalizations and 50,000 deaths annually, according to the U.S Department of Health and Human Services. In the hours following a TBI, blood and cerebrospinal fluid accumulate in the area around the primary injury, increasing intracranial pressure. If the pressure of brain tissue and fluid exceeds the pressure of the brain’s blood supply, brain tissue can become de-oxygenated. This can lead to a secondary traumatic brain injury. Currently, secondary traumatic brain injury is diagnosed using an intracranial pressure sensor. However, because brain tissue is very compliant, a significant amount of fluid can accumulate near the injury before the intracranial pressure detects a change. By the time current instruments diagnose an injury, significant damage may have already occurred. There is a clinical need for an instrument able to provide an earlier diagnosis for secondary traumatic brain injury.

Tracking a patient’s brain compliance shows promise as a method for early detection of secondary traumatic brain injury. Our sponsor believes that comparing the intracranial pressure and electrical impedance will provide an indirect measure of brain tissue compliance. Electrical impedance and intracranial pressure both have periodic waveforms. In healthy tissue, there is a phase delay between these two waveforms. As injuries worsen, the compliance decreases and the phase delay between the impedance and pressure waveforms decreases. Therefore, continuous monitoring of the phase delay should provide an indirect estimate of the tissue compliance.

Our goal was to develop a bench-top model that reflects the relative changes in impedance, pressure, and compliance, and to collect sufficient data to prepare an Institutional Animal Care and Use Committee (IACUC) proposal so our sponsor can conduct animal testing in the future.

We designed a test bed that models the brain with a large piece of porous foam encased within an acrylic tank. Saline solution, representative of blood and cerebrospinal fluid, is pumped into the foam with a pulsatile flow pump. Saline flows from the tank into a reservoir, for recirculation. A secondary reservoir held above the tank models the small fluid reserve at the base of the skull. Electrical impedance was calculated between two brass electrodes fixed within the foam. Pressure data was collected from a fiber optic sensor inserted into the foam. A porous, acrylic plate is used to compress the foam to different levels, changing the compliance of the foam.

Initially, the noise in the impedance signal prevented us from evaluating changes in phase delay. However, after redesigning our electrodes, time averaging our impedance data, and using tap water instead of saline, we acquired a periodic impedance waveform. Despite numerous tests and iterations, we have not yet detected a compliance-based change in the phase shift between pressure and impedance waveforms. Future work includes testing lower compliance materials that more accurately model the brain, redesigning the test bed for easier operation, and more precisely representing the small-scale hydrodynamics of the brain.

Hip Locking Mechanism

Each year, 332,000 total hip arthroplasties (THA) are performed in the United States. The implant used in THA is comprised of an acetabular metal shell and polyethylene liner and a femoral head, neck, and stem. Our sponsor, a patient-specific orthopedic implant company, is exploring the hip implant market and tasked us with developing a novel locking mechanism between the acetabular liner and shell. Our deliverables were CAD designs of the locking mechanism, physical prototypes of the acetabular shell and liner, and validation test procedures and data. The group identified rim fracture as an unaddressed failure mode in state-of-the-art locking mechanisms, and determined its root cause to be the placement of stress risers in the locking mechanism geometry at the rim of the liner. Thus, we set out to design an acetabular locking mechanism that reduces stress concentrations at the rim of the liner and performs at least as well as state-of-the-art designs on three clinically relevant ASTM validation tests.

We designed a novel locking mechanism and fabricated metal shell and plastic liner prototypes. Our prototypes, even without being fabricated from high performance final materials, performed within the state-of-the-art value ranges for three key ASTM validation tests: axial disassembly, torque out, and offset pull out. To examine stress concentrations under femoral neck impingement compared to the state-of-the-art, we replicated a Finite Element Analysis (FEA) conducted in the literature on liners that were revised due to rim fracture. The same FEA conditions were applied to the proposed design to demonstrate that it reduces stress concentrations compared to the state-of-the-art. Our design is novel, reduces stress concentrations that can lead to rim fracture, and performs comparably to the state-of-the-art on clinically relevant ASTM validation tests.